On 5/30/2013 1:55 AM, Gerrit Heitsch wrote: > On 05/30/2013 08:22 AM, Jim Brain wrote: >> Speaking (writing) of bank registers, anyone know of a TTL option that >> has a falling edge trigger? Yes, I can do an inverter, but would rather >> not. Use case is VIC-20, which won't work on rising edge of Phi, >> because not all of the data is valid on rising edge. > > The 74LS373 or 74LS573 does that. But it's a latch, not a register. > They use it in the C64 to de-multiplex the VIC address so it can > access the char ROM. Trigger is the falling edge of _RAS. > > Now you have to check if a latch works in your case. A latch (in general) would work in this case, as the outputs don't need to be valid until PHI2 goes high again, which would be 500nS later. Thus, I appreciate the suggestion. But, as I look at replacing, I realize I forgot the latch needs an enable line as well. Neither of those offer one. I'm trying to create a "register" at Address 38920 (on the VIC) to hold the FLASH ROM bank. I have 38920 decoded as active low, and then an inverted PHI into the CLK line of a '173 is latching the bank. But, I'd rather use a single IC solution. JIm Message was sent through the cbm-hackers mailing listReceived on 2013-06-04 02:00:03
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